Effective playing time affects technical-tactical and physical parameters in football

Effective playing time has been debated as a topic of major concern in football. Thus, the current experimental study aimed to investigate the effects of effective playing time on technical-tactical and physical match parameters in football. One hundred and seventy-nine male highly trained football players (aged 27.9 ± 5.1 years) from twelve teams performed two different match-play conditions: 45 min of match-play without stopping the chronometer (T45), and 30 min of match-play by stopping the chronometer every time the ball was out-of-play (T30). T30 presented a significantly higher total time (49:30 vs. 45:00 min; p = <.001; ES = 0.76), effective playing time (28:70 vs. 26:80 min; p = <.001; ES = 0.62), and stopped time (20:60 vs. 18:20 min; p = 0.003; ES = 0.38) compared to T45. Total ball possession (54.4% vs. 45.6%; p = 0.002) and 1/3 ball possession (55.3% vs. 44.7%; p = 0.018) was higher in T30 condition when compared to T45. Regarding match external load, total distance covered (4,899 vs. 4,481 m; p = <.001; ES = 0.71), moderate-speed running (607 vs. 557 m; p = 0.002; ES = 0.26) and high-speed running (202 vs. 170 m; p = <.001; ES = 0.33), high-speed activities (284 vs. 245 m; p = 0.003; ES = 0.24), accelerations (27 vs. 24; p = <.001; ES = 0.32), and decelerations (31 vs. 28; p = 0.005; ES = 0.26) were higher in T30 compared to T45. In conclusion, these findings suggest that higher effective playing time may affect technical-tactical and physical parameters during football games.


Introduction
Football match-play has been considered as a complex, self-organised, unstable, unpredictable, and highly dynamic system, in which coaches and players try to keep the stability of their own attacking and defending system and to disorganize the opponents' structure (1-3). However, several contextual factors, such as match location, competition features, team ranking, level of play, match outcome, and style of play may influence individual and team behaviors (4)(5)(6)(7)(8). Consequently, players must adapt physically, physiologically, and psychologically to different match-related contextual factors, which may lead to changes and variations in technical-tactical actions and patterns during match-play (3).
Football interruptions are a main characteristic of a match and may underline the intermittent nature of sport (9)(10)(11). Recently, effective playing time has been debated as a topic of major concern by several stakeholders in football (10)(11)(12)(13), as official matches last for >90 min, however several interruptions, such as substitutions, fouls, injuries, goals, or the ball being out-of-play could negatively affect the effective playing time (9,14). For example, it has been found in the Portuguese League that effective playing time was on average −49 min of total playing time (i.e., 90 min), which is consistently lower compared to other European Leagues (i.e., Germany, Spain, France, England, and Italy) and the Champions League (15). Given that, a recent study (16) considering the effective playing time, distinguishing the two main phases of the game (i.e., possession or non-possession of the ball), and normalizing the total distance to meters per minute (m·min −1 ), found that teams run more without possession than in the ball-possession, and the effective playing time and the amount of ball possession influenced the players' running performance. Another study (17) investigated the effects of the Video Assistant Referee system (VAR) on the playing time, technical-tactical, and physical performance in soccer players, and found that the total playing time increased slightly when compared to three situations (without the intervention of VAR = 95.1 min, one intervention of VAR = 96.0 min, and 2-3 interventions of VAR = 99.1 min), however, effective playing time decreased significantly between without VAR and one intervention of the VAR (52.5 vs. 51.5 min). Considering technical-tactical parameters, in the same study (17) the total scored goals increased as the number of VAR intervention increased.
Regarding the match demands during effective playing time, professional players competed in the German Bundesliga covered on average 10% more total distance, and performed 13% more accelerations, while sprinted 7%-10% less in official matches with long (>65 min) compared to short (<50 min) effective playing time (12). Moreover, professional soccer players of the English Championship presented lower physical match demands comparing whole match metrics compared to the ball was in play metrics (18). Similar results found in youth elite soccer players (19). Considering effective playing time and contextual factors, such as team's level, match result and location, total distance was greater when playing at home, when the team was losing, and when the level of the opposing team was higher (20). However, more research is warranted about the effects of effective time on physical and technical-tactical parameters during football matches.
Other team sports (e.g., futsal, basketball) can be a benchmark for effective playing time, because the time is stopped when the ball is out-of-play. In football, however, several contextual variables may affect effective playing time. Therefore, the current study aimed to explore the differences on match-play time-related variables (i.e., total, effective, and stopped time), technical-tactical parameters (e.g., ball possession, shots to the goal), external load metrics, and other match-related events (i.e., medical assistance, goal-kicks, corners, throw-ins, kick-offs, free kicks) in two different match-play conditions: 45 min of match-play without stopping the chronometer when the ball was not in-play (T45), and 30 min of match play stopping the chronometer every time the ball was out-of-play (T30). The players, coaches, and referees were unaware about the way playing time had been counted, and only an external timekeeper was responsible for the time counting during match play. It was hypothesized that T30 would present higher time-related variables, technical-tactical parameters, and external load metrics when compared to T45.

Study design
An experimental observational study was designed. Match-play data from 6 friendly games were collected. Matches were randomly divided into a 45-min half (T45; 45 min of match-play without stopping the chronometer when the ball was not in-play), or a 30-min effective-time half (T30; the chronometer was stopped every time the ball was out-of-play). An overall of six halves of T45 and six halves of T30 was analyzed for the current study. All games had official football referees (i.e., one main referee, and two assistant referees), but an external timekeeper was responsible for the time count during the match play. An official futsal timekeeper was responsible for the chronometer (Keenso PC3830A, USA), and provided no feedback to the participants during the experiment. Between each half, there was a 15-min half-time; during this break, no feedback has been provided to the participants by the timekeeper. All games were played by the end of the season 2021-2022.

Participants
One hundred and seventy-nine male amateur highly trained football players [i.e., Tier 3: Highly Trained/National Level (21)] (aged 27.9 ± 5.1 years) from twelve teams competing in the 4 th and 5 th tier in Portugal (regional level) participated in the experiment. All players had >18 years old and had been involved in 3-4 training sessions per week and one weekly official match during the season 2021-2022. Goalkeepers were excluded from the study because of the different technical-tactical and physical match demands. Prior to participation, the study design and objectives were carefully explained to the players, referees, and teams' staff. The participants then signed an informed consent. The study was approved by the Ethics Committee of the Portugal Football School (n°15/CEPFS/2022).

Procedures
All games were recorded using a 35-megapixel camera (Canon XA15Hd, Japan). The camera was placed above the field to record the entire pitch throughout the entire duration of the match. The matches were analysed and coded with LongoMatch software (Barcelona, Spain). Three categories of variables were used: timerelated variables, match events related with stopped time, and offensive technical-tactical variables ( Table 1).
The players wore GPS units (APEX, STATSports, Northern Ireland) with a sampling frequency of 10 Hz. Each player wore a tight vest with the GPS unit on the back of their upper body between the scapula as described by the manufacturer. The devices were activated 15 min prior to the start of each match; this period has been excluded from analyses, and only data from players playing full matches were included. Doppler derived speed data was exported from manufacturer software (STATSports Sonra

Statistical analyses
A statistical package (The jamovi project. (2022). jamovi. (Version 2.3) [Computer Software] https://www.jamovi.org) was used for the statistical analysis. A descriptive statistic with mean and standard deviation (SD) was performed for all variables. A linear mixed model was used to examine the differences in external load variables between T30 and T45, accounting for individual repeated measures. A general linear model was used to analyse the differences between the actions and mean stopped time between games T30 and T45. One sample proportion test was used to compare the offensive technical-tactical variables between the two conditions. Cohen's d effect sizes and 95% confidence intervals (CI) were performed, and interpreted as follows: <0.2 = trivial; 0.20 = small; 0.50 = moderate; and 0.80 = large (24). A significance level was set at p < 0.05.

Discussion
This experimental study aimed to explore the effects of effective playing time in several technical-tactical and physical parameters in football match. The main findings were that T30 presented higher total, effective, and stopped time when compared to T45. A total Technical-tactical  Frontiers in Sports and Active Living ball possession and 1/3 possession higher percentage in T30 compared to T45. Lastly, T30 presented higher external load metrics (i.e., total distance, moderate-and high-speed running, high-speed activities, accelerations, decelerations) when compared to T45. Therefore, the results of higher effective playing time may affect technical-tactical and physical parameters during football games. Considering time related variables, T30 presented significant higher total, effective, and stopped time compared to T45. However, no significant differences were found when effective playing time was calculated as a percentage of the total time. To the author's knowledge this is the first experimental study that compares two different time protocols (T45 vs. T30) and time related variables. Furthermore, Errekagorri et al. (17) demonstrated that the total playing time increased slightly when compared to three situations (without the intervention of VAR = 95.1 min, one intervention of VAR = 96.0 min, and 2-3 interventions of VAR = 99.1 min), however, effective playing time decreased significantly with intervention of the VAR (51.5 min) when compared without VAR (52.5 min). Therefore, more research about the influence of player's behavior about time consuming during official matches with and without stopping the chronometer when the ball was out-of-play is warranted.
In recent years, it has been considered these technical actions as key determinants of performance (16,25,26). Bush et al. (27) identified limited influence from match-related contextual variables (i.e., game location, final result, and opponents' level) on technical parameters (i.e., number of passes and shots on goal); however, shots, shots on target, and assists were noted has technical actions that displayed high match-to-match variation, which indicates that these variables were sensitive measures. Differently, Liu et al. (28) suggest that match-to-match variation of players' technical performances is affected by different match contexts. Thus, caution should be taken when using these variables to assess and interpret players' match performance, for consideration, long-term analysis seems to lead to a decrease in the impact of match-related variables on technical parameters (29). In the current study total ball possession and 1/3 ball possession were significantly higher during T30 when compared to T45. Previous studies considered a greater possibility of finishing successfully the attack when the ball carrier is closer to the opponent's goal (30, 31). However, higher ball possession did not significantly affect the number and the proportion of shots within area and out of area, during T30 compared to T45. Considering technical-tactical parameters, a recent study (17) presented the total scored goals increased as the number of VAR intervention increased (without VAR intervention = 1.2 goals; one VAR intervention = 1.5 goals; 2-3 VAR interventions = 1.7 goals). Moreover, regarding offensive variables, it has been indicated that teams' performance mainly results from the ability to manage the game, keep ball possession, and create shots opportunities (32). Currently, studies on the success of football teams showed that the effectiveness and quality of the shots rather than the number and quantity determine the final score of the match (25,26,28,(33)(34)(35).
Considering external match load metrics, players covered more total distance, moderate-and high-speed running, and performed more high-speed activities, accelerations and decelerations during T30 compared to T45. These results are in line with previous studies in elite and youth soccer players (12,(18)(19)(20). Specifically, effective playing time influenced physical match performance, with total distance and accelerations being the most affected (r = 0.48-0.61), and high-intensity and sprinting distance, and maximum velocity the least affected parameters (r = −0.17-0.03) (12). Furthermore, players covered on average 10% more total distance and performed 13% more accelerations, while sprinting 7-10% less in matches with long (>65 min) compared to short (<50 min) effective playing times (12). These results could be explained by the higher total and effective playing time. The results reported by Peñas et al. (34), are in line with the current study, that higher physical demands in the first half might be related with higher effective playing time when compared to the second half of the   (13) found that effective playing time should be considered when interpreting the match running performance on professional soccer players, as non-significant differences on high-speed running and sprinting distances were found between the 1st and 2nd halves in professional soccer players when the effective playing time was considered. Lastly, another study (36) showed that total distance and relative total distance significantly decreased in seasons with VAR compared to seasons without VAR in the top Spanish professional football league. Consequently, higher effective playing time may increase the physical match demands, but more research is warranted on this topic. Whilst this is the first experimental study to explore different time methods (T30 and T45) on effective playing time in football games, the experiment is not without limitations. Contextual factors such as the phase of the season (i.e., beginning, middle, or end), relative importance of the game, match location (i.e., home or away), match score, classification and the level of the opponent team, as well as players' position, were not considered. Another limitation is the number of games (n = 6) performed. In this study, the players, staff, and referees were unaware of the type of the game (T30 and T45) and the time regulation, and only two types of games were designed. More research about the effects of different time regulations on technical, tactical, physical, and psychological parameters is needed. Also, future studies can split the data into 15 min periods and consider the score influence.
In summary, T30 presented a significantly higher total time, effective playing time, and stopped time compared to T45. Players had significantly higher total ball possession and 1/3 ball possession, and covered a significantly higher total distance, moderate-speed running, high-speed running, and performed more high-speed activities, accelerations and decelerations in T30 compared to T45. Furthermore, these findings suggest that the effective playing time may have meaningful effects on technicaltactical and physical parameters during football games. Therefore, international organizations should have on mind that implementing a stopped clock during football matches, this regulation may change the teams and players' technical-tactical behavior, and consequently the match demands.

Data availability statement
The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Ethics statement
The requirement of ethical approval was waived by the Ethics Committee of the Portugal Football School (n15/CEPFS/2022). The studies were conducted in accordance with the local legislation and institutional requirements. Written informed consent for participation was obtained from the participants.

Author contributions
OT and JB contributed to conception and design of the study. OT, JT and PP collected the data. OT and KS organized the database. KS performed the statistical analysis. OT and KS wrote the first draft of the manuscript. OT, KS, JT, PP and JB wrote sections of the manuscript. All authors contributed to the article and approved the submitted version.

Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.